The present invention relates to methods for the separation of titanium from ore, especially iron-bearing ore e.g. ilmenite ore. In embodiments of the invention, the method relates to the recovery of titanium tetrahalides, especially titanium tetrachloride from solutions. In further embodiments, the invention relates to recovery of titanium metal from such ore.
Many processes are known for the recovery of titanium dioxide from ores. Ilmenite, which contains mainly titanium oxide and iron oxide values, often is employed in such processes. The majority of processes for the recovery of titanium dioxide from ores involve digestion of the ore in a mineral acid, such as hydrochloric acid or sulphuric acid, to remove at least the titanium values from the ore. In such processes, however, the purity of the titanium dioxide produced is about 90-95%, and hence further purification procedures may be required to produce a pigment grade product, which adds considerably to the cost. Many of the further purification procedures involve techniques that are environmentally unacceptable without extensive procedures to treat various solutions and solids obtained. Such treatment processes tend to be costly.
Processes for the recovery of titanium dioxide from ilmenite in high purity and high yield are known. One such process is described in U.S. Pat. No. 3,903,239 of S. A. Berkovich, which discloses a process which comprises contacting ilmenite, or a concentrate thereof, in particulate form with concentrated hydrochloric acid at a temperature of about 15-30xc2x0 C. to solubilize and leach from the ore at least 80%, preferably at least 95%, of the iron and titanium values. The leaching operation may be carried out over an extended period of time, typically from 3-25 days, depending on the technique employed and the quantity of iron values to be recovered. Leaching techniques include counter-current flow or the use of closed cycle loops in which hydrochloric acid is continuously passed through a bed of the ore. The leaching operation is exothermic, and the reactants are maintained in a temperature range of 15-30xc2x0 C. by cooling, if necessary.
The ilmenite or similar ore used in the process may be treated as such or may be beneficiated to form a concentrate in any desired manner. Ilmenite generally contains TiO2.FeO with varying amounts of Fe2O3 and gangue materials, usually silicates, alumina, lime and magnesium. Beneficiation may be employed when the ore is of low TiO2 content.
The ore or concentrate may be pre-treated prior to contact with the concentrated hydrochloric acid to increase the rate of dissolution of the titanium and iron values during the leaching step. Such pre-treatment may include an initial oxidation at elevated temperature, such as from 600-1000xc2x0 C., in the presence of air and/or oxygen to split the TiO2.FeO followed by reduction of at least part of the iron oxide with carbon or carbon monoxide. This is a smelting step, with slag from the smelting step being fed to the leaching step and pig iron being marketed.
Subsequent to the leaching step, it is necessary to convert any ferric iron in the solution to ferrous iron, which is typically achieved by reduction of the ferric iron in the leach liquor with a gaseous reducing agent e.g. sulphur dioxide. The conversion of ferric iron to ferrous iron in this manner is essential in view of the affinity of titanium dioxide for ferric iron and the difficulty in separating ferric iron from titanium dioxide.
The solution of titanium chlorides and ferrous chloride which is thus obtained, and which may contain minor quantities of gangue metal chlorides, typically calcium and magnesium materials, is then mixed with water to cause hydrolysis of the titanium chlorides. A seeding amount, generally about 1-2%, by weight of the titanium oxyhydrate to be precipitated (TiO2.3H2O) is included in the mixture. Titanium oxyhydrate precipitates from the mixture. The hydrolysis is carried out using a quantity of water at least sufficient to precipitate substantially all of the titanium values from the solution but insufficient to cause precipitation of other metal oxides or hydroxides. The titanium oxyhydrate that is precipitated from the mother liquor is then washed substantially free of entrained mother liquor and dried. The washed precipitate is converted at elevated temperature, typically 700-1000xc2x0 C., in the presence of air and/or oxygen into the anatase or rutile form of titanium dioxide.
Alternative methods that require less treatment of solution and solids to ensure environmental acceptance and/or are less expensive in achieving environmental acceptance, as well as producing titanium and other products of high value e.g. high purity, are required.
A method for the separation of titanium, and for production of titanium metal, from titanium-bearing ore that involves a reduced number of steps has now been found.
Accordingly, one aspect of the present invention provides a method for the separation of iron values from titanium-bearing ore, comprising the steps of:
a) leaching said ore, or a concentrate thereof, with an aqueous solution of a hydrogen halide;
b) separating solids from the leach solution obtained in (a), to provide a leachate solution;
c) subjecting the leachate solution to extraction with an immiscible organic phase that selectively extracts iron values into said organic phase, titanium values in the leachate solution selectively remaining in the aqueous leachate solution.
Another aspect of the invention provides a method for the production of titanium metal from titanium-bearing ore, comprising the steps of:
a) leaching said ore or a concentrate thereof with an aqueous solution of a hydrogen halide;
b) separating solids from the leach solution obtained in (a), to provide a leachate solution;
c) subjecting the leachate solution to extraction with an immiscible organic phase having a boiling point that differs from the boiling point of the titanium halide in the leachate by an amount that permits separation thereof by fractional distillation, said organic phase being stable with respect to the titanium halide; and
d) stripping titanium halide from the organic phase obtained in step (c) by heating to volatilize the titanium halide and effect separation from the organic phase.
A further aspect of the invention provides a method of separating a titanium halide from a concentrated aqueous solution of the titanium halide, said titanium halide being in a concentration such that the titanium halide is substantially stable in said aqueous solution, comprising:
a) admixing said aqueous solution with an organic phase having a boiling point that differs from the boiling point of the titanium halide by an amount that permits separation thereof by fractional distillation;
b) separating the organic phase so obtained from the aqueous solution; and
c) heating the organic phase and stripping titanium halide therefrom.
Yet another aspect of the invention provides a method for the separation of titanium from a titanium-bearing ore, said ore containing iron, comprising the steps of:
a) leaching said ore, or a concentrate thereof, with an aqueous solution of a hydrogen halide in the presence of an oxidising agent; and
b) effecting a separation of titanium dioxide obtained in step (a) from said solution.
A further aspect of the invention provides a method of forming a titania-rich slag from a titanium-bearing ore that contains iron, comprising the steps of:
a) calcining the ore under oxidizing conditions to eliminate sulphur from said ore, said calcining being carried out at a temperature of at least 1200xc2x0 C.;
b) subjecting the hot calcined ore of step (a) to reducing conditions in the presence of CO;
c) transferring the hot reduced calcined ore obtained in step (b) to a smelting step;
controlling the reducing conditions and the smelting step to obtain pig iron and a titania-rich slag with a predetermined iron content.
Another aspect of the invention provides a method of forming a titania-rich slag from a titanium-bearing ore that contains iron, comprising the steps of:
a) calcining the ore under oxidizing conditions to eliminate sulphur from said ore, said calcining being carried out at a temperature of at least 1200xc2x0 C.;
b) subjecting the hot calcined ore of step (a) to reducing conditions in the presence of CO;
c) transferring the reduced calcined ore obtained in step (b) to a leaching step in an aqueous solution of weak sulphuric acid;
controlling the reducing and leaching conditions to obtain a titania-rich material having less than 5% by weight of the iron content of the ore.
A further aspect of the invention provides a method for the separation of iron and titanium values from an iron/titanium ore, comprising the steps of:
a) leaching said ore, or a concentrate thereof, with an aqueous solution of a hydrogen halide in the presence of an oxidising agent; and effecting a separation of titanium dioxide obtained from said solution.
b) subjecting the aqueous leach solution so obtained to extraction with an immiscible organic phase that selectively leaches iron values into said organic solvent.
Yet another aspect of invention provides a method for the separation of iron values from titanium-bearing ore, comprising the steps of:
a) leaching said ore, or a concentrate thereof, with an aqueous solution of a hydrogen halide;
b) separating solids from the leach solution obtained in (a), to provide a leachate solution;
c) subjecting the leachate solution to extraction with an immiscible organic phase that selectively extracts iron values into said organic phase, titanium values in the leachate solution selectively remaining in the aqueous leachate solution.
d) subjecting the aqueous raffinate so obtained to steps to separate TiO2 therefrom.
Processes for the recovery of titanium dioxide from ilmenite, with high purity in high yield, are known. Techniques for treating the ilmenite ore, optionally to form concentrate and/or for beneficiation of the ore are known. In some instances, it is possible to treat the ore or concentrate with concentrated hydrochloric acid solution to effect a leaching of titanium values from the ore or concentrate. In other instances, it is necessary or desirable to subject the ore or concentrate to a smelting step in the presence of carbon and/or fluxing agents, and to then separate a slag from the smelting process which is then subjected to the leaching step.
One aspect of the present invention is directed to the step of recovery of titanium values from the leaching solution. The leaching solution is a mixture of aqueous hydrochloric acid containing titanium values, and other soluble material and solid materials, particularly residues of the concentrate and/or slag from which the titanium values have been leached. A liquid/solid separation step is conducted, to separate a leachate solution from solids.
The leachate so obtained is treated, according to an aspect of the present invention, with an organic phase. The titanium values in the leachate are in the form of titanium halide, especially titanium tetrahalide which, if hydrochloric acid is used in the leaching step, will be titanium tetrachloride.
In one aspect of the invention, the organic phase is selected so that iron values are selectively separated into the organic phase. Thus, an organic/aqueous separation is effected, with the iron values being in the organic phase and titanium values remaining in the aqueous phase. Preferably, iron values are separated almost to the exclusion of other values in the leachate solution, or with values readily separated therefrom, so that iron products especially iron oxides, may be obtained in high purity. Vanadium and other metal values that may be present in the leachate are preferably retained in the aqueous phase.
Examples of the organic phase are phosphoric, phosphoric acid and phosphinic acids, esters oxides thereof. Specific examples are tri-n-butyl phosphate and di-2-ethylhexyl phosphoric acid. The organic phase preferably contains a diluent e.g. a hydrocarbon, an example of which is a kerosene.
The organic phase may be stripped from the iron values and recycled. The iron values may then be subjected to pyrohydrolysis, or other steps, to recover iron e.g. as iron oxides. Preferably HCl is obtained as a by-product which is recycled to the step of leaching of ore or concentrate described above.
In a second aspect, the organic phase is selected such that the titanium halide is soluble in the organic phase. Moreover, the organic phase is selected such that the organic phase and titanium halide may be separated by fractional distillation. The organic phase may be selected to have a higher or lower boiling point that the titanium halide. The preferred titanium halide is titanium tetrachloride. In embodiments of the invention, the boiling point of the organic phase differs by least 50xc2x0 C., and especially at least 75xc2x0 C., from the boiling point of the titanium halide. The organic phase must be immiscible with the aqueous solution, such that it forms a second layer so that separation may be effected.
The titanium halide is extracted from the aqueous solution into the organic phase, to effect removal of the titanium halide from the aqueous solution. Such extraction may be carried out in a continuous operation or in a batch operation.
The organic phase may be, for example, a crown ether, phosphine acid, ester or oxide, or tertiary or quarternary ammonium salt.
The organic phase containing the titanium halide is separated from the aqueous solution and from any solid matter, and is then subjected to a step to separate the titanium tetrachloride. In the separation step, the organic phase containing the titanium halide is heated to effect the separation of the titanium halide. This is preferably accomplished by volatilization of the titanium halide, especially if the halide is chloride although for any particular tetrahalide the organic phase may be selected to effect volatilization of either the titanium tetrahalide or the organic phase. In addition, the organic phase should be selected so that it has a flash point that is acceptable under the operating conditions, preferably a flash point above the temperature used in separation. The organic phase needs to be stable with respect to the aqueous solution and to the titanium tetrahalide at the operating conditions.
The aqueous solution remaining after extraction may be subjected to known procedures for recovery of iron or other metal values or procedures described above, and for recovery and recycle of acid used in the leaching step. For example, iron oxide (Fe2O3) may be recovered and the acid e.g. HCl, recycled. The organic phase is preferably recycled back to the extraction step, and reused.
The titanium tetrahalide may be subjected to purification steps, if necessary. However, if the titanium tetrahalide is volatilized, it may be of acceptable purity for many end-uses. The titanium halide may be used as such or subjected to further processing steps e.g. to form titanium metal. Techniques for the conversion of titanium tetrahalide and titanium dioxide to titanium metal are known.
In embodiments of the invention, essentially all of the iron of the feed material i.e. titanium-bearing ore or concentrate is dissolved by the HCl. Thus, sufficient HCl has to be provided. In order to minimise the amount of HCl required in the process, the iron chloride (e.g. H+FeClxe2x88x924 or a chloride of iron e.g. FeCl3) produced in the process is subsequently subjected to pyrohydrolysis to regenerate the HCl. The iron is converted into an iron oxide product (Fe2O3). By controlling the composition of the iron chloride solution before subjecting it to pyrohydrolysis, it is possible to produce a high grade iron oxide suitable for use in pigment production. If this is not economic, the disposal of iron oxide becomes an environmental problem. In such instances, it is advantageous to remove the iron and upgrade the titanium ore before subjecting it to treatment with HCl. This alternative also has the advantage of decreasing the size of the hydrometallurgical plant for a given production of titanium.
In another aspect of the present invention, the ore or concentrate is leached in aqueous solution in the presence of an acid and an oxidizing agent. A variety of oxidizing agents may be used, including air, hydrogen or other peroxides, or sodium or other perchlorates. The oxidizing agent should be selected to minimize any contamination of the solution with cations that have an adverse effect on other process steps.
In the aqueous solution, the titanium is converted to titanium dioxide and the iron is solubilized. The acid is preferably a hydrogen halide, especially HCl. If the acid is HCl, the concentration of acid may be controlled, in the presence of the oxidizing agent, to convert iron into H+FeClxe2x88x924, which is soluble in the aqueous solution. Subsequently, liquid/solid separations may be effected, to separate TiO2 including separation of TiO2 from tails from the aqueous solution. The aqueous solution may be treated for recovery of HCl and iron e.g. as Fe2O3.
One of the concentration alternatives for the treatment of the ilmenite ore or physically beneficiated ilmenite is the production of a titanium-rich slag and pig iron from it, with the titanium-rich slag being subjected to HCl leaching for titanium recovery and the iron being sold as a foundry-grade pig iron.
The processing of ilmenite to produce titania slag and pig iron is known. In such processing, the concentrate is calcined in a rotary kiln under oxidising conditions at about 1200-1300xc2x0 C. to eliminate sulphur in the ilmenite concentrate. The product is cooled and fed to an electric furnace with coal/coke as reductant to reduce the iron and produce a molten slag and pig iron. The electric furnace smelting takes place at about 1650xc2x0 C. Disadvantages of the current processing method include (i) the energy in the calcine from the rotary kiln is lost and the product must be re-heated to the smelting temperature in the electric furnace with electric power; (ii) the reduction in the electric furnace produces a lot of CO gas, which often results in the foaming of the slag and process control is difficult; and (iii) the reduction of the iron oxide by carbon to produce CO is endothermic and the heat required is supplied by electricity.
The production of electricity from fuel is typically energy inefficient, to the extent of about 30% conversion, and therefore the process is very energy intensive.
In aspects of the present invention, the use of energy is reduced. In a preferred embodiment, the reduction of the calcine is carried out prior to the electric furnace smelting. This may be carried out in a second reducing section of the calcining kiln or a separate kiln following the calcining kiln. The reduction is done by reducing gases produced by the partial reduction of CO (produced in the electric furnace) and/or by partial combustion of fuel. The reduced calcine so produced is transferred hot from the reduction kiln to the electric furnace, with any additional reductant if required. This saves the energy lost in cooling the calcine and improves the efficiency of use of fuel for the iron oxide reduction. The smelting of reduced calcine requires less electric energy, produces very little gas in the electric furnace and makes the electric furnace easier to control. The reduction in the reduction step and the electric furnace are controlled to provide a desired iron level in the slag. This controls the slag melting temperature. Depending on the composition of the ilmenite concentrate, the smelting may be carried out at lower temperatures e.g. 1550xc2x0 C., thereby conserving more energy compared to the current processing.
Alternatively, the process of smelting and production of molten titania-rich slag and pig iron in the final step of the above process may be replaced by a leaching process for removing the reduced iron produced in the reduction step. This may be carried out by dissolving it in a weakly acidic chloride solution, with aeration, to dissolve the iron and leave a titania-rich oxide product suitable for HCl leaching, as described herein. The advantage of this approach is that the reduction can be carried out at lower temperature e.g. about 800xc2x0 C. instead of about 1000xc2x0 C. and the energy of smelting in the electric furnace is conserved. In addition, in this embodiment, it is possible to eliminate over 95% of the iron and minimise the iron fed to the HCl leaching process. In comparison, there is about 90% iron removal in the smelting route, as some iron has to be left behind to provide a fluid slag in the smelting step. This minimises the usage of HCl and the subsequent regeneration of the HCl for re-use in the process.
In the production of titanium and TiO2 pigment, it is necessary to produce titanium chloride by chlorination of titanium dioxide-containing materials e.g. titania slag and rutile concentrate, at about 900xc2x0 C. in the presence of coke. By using the present process, the titanium chloride may be produced by leaching the titania containing material with HCl followed by extraction and separation of titanium chloride. The high temperature chlorination is replaced by lower temperature operations and avoids the formation of environmentally unacceptable dioxins which can form in the high temperature chlorination. In addition, the purity of the titanium chloride produced in the present process will be improved and will require less purification or even no purification.
In various aspects of the invention, there is provided a process in which titanium-bearing ore or concentrate, generally after having been subjected to a smelting step, is subjected to a leaching step using aqueous hydrochloric acid. A leach solution containing titanium and iron values, and other metallic values depending on the particular ore, is obtained. A liquid/solid separation step is conducted. The solids may be subjected to other separation steps but generally will be gangue.
In preferred aspects of the invention, the leachate solution is subjected to extraction with organic phase to extract iron values, as described above. Such phase may contain 100-200 g/l of iron, or more. Examples of the organic phase are tri-n-butyl phosphate and di-2-ethylhexyl phosphoric acid, with other examples being described above. The organic phase with iron values is then subjected to steps to separate and recover the organic phase, which is recycled to the step of extraction of the leachate solution. Iron values, which are in the form of chlorides are recovered, especially by pyrohydrolysis to yield iron oxides and HCl. The HCl is recycled to the leaching of the ore or concentrate. Iron values of high purity may be obtained.
The leached aqueous solution or raffinate may be treated to separate vanadium and other metallic values, depending on the particular ore, especially by precipitation, to provide a raffinate rich in titanium, and preferably with high-purity titanium values. The titanium values are in the form of the chlorides viz TiCl4, which may be subjected to steps to form TiO2, which is recovered. High purity TiO2 may be obtained, which may be of sufficiently high purity for use as such.
As an alternative, the raffinate rich in titanium values may be subjected to further extraction, using an organic phase that is immiscible in water and which has a boiling point that differs from the boiling point of the titanium value, e.g. titanium tetrachloride by an amount to permit fractional distillation. The titanium value is extracted from the aqueous solution of the raffinate into the organic phase and then recovered by distilling or flashing off either the organic phase or the titanium value, depending on the respective boiling points. Titanium metal may then be recovered from the titanium halide.
The by-products of such a process are minimized, and may be treated by known but relatively simple techniques.
An alternative separation of titanium values is to separate the titanium as TiO2 directly from the leaching of the ore or concentrate, by leaching in the presence of an oxidizing agent and separating the TiO2 formed from the solution and from other solids therein.
The present invention provides methods for the separation of titanium from titanium-bearing ores, especially ilmenite. In particular, the invention provides methods for production of titanium tetrahalides, especially titanium tetrachloride, and TiO2 with improved purity and/or such that related steps in an overall process, including recovery and recycle of materials, may be simplified and be more cost effective. In particular, the volumes of liquid and solids that must be handled in the overall separation process may be reduced, and associated hardware may be reduced in size. Such improvements may be of significant economic benefit.